1. Field of the Invention
The present invention relates to a control apparatus for controlling an operation of an automatic transmission for a vehicle, and more particularly, to a control apparatus for disengaging a lock-up clutch when an abrupt brake is applied in order to prevent an engine stall.
2. Background Art
Japanese Patent Application Laid-open No. Toku Kai-Hei 2-227342 discloses a drive system having a torque converter with a lock-up clutch, a planetary gear type forward and reverse changeover apparatus and a continuously variable transmission (CVT). The drive system is designed to disengage the lock-up clutch of the torque converter when an anti-lock brake (ABS) operates, that is, when the wheel slip is properly controlled, so that an engine stall is prevented.
However, particularly when a vehicle is abruptly braked on a road surface having low friction coefficient, even if the vehicle is equipped with ABS, depending upon braking conditions, there is a possibility that a wheel is locked to stop the rotation before the lock-up clutch is released and as a result an engine stall occurs.
In order to solve this problem, Japanese Patent Application Laid-open No. Toku-Kai-Hei 4-357357 proposes a drive system in which both forward clutch and reverse brake of the forward and reverse changeover apparatus are set to a disengagement condition. However, releasing both of the forward clutch and reverse brake may cause an overrun of the engine, in case where a driver depresses an accelerator pedal to accelerate the vehicle immediately after an abrupt braking.